1. Field of the Invention
The present invention relates to an exposure technique and, more particularly, to a photomask and a method of manufacturing a semiconductor device using the photomask.
2. Description of the Related Art
In recent years, the feature sizes of semiconductor devices decrease, and the pitch of a mask pattern formed on a photomask also decreases. When the pitch of the mask pattern on the photomask becomes about 4 times or less the wavelength of irradiation light, the diffraction efficiency starts to change depending on the polarization direction of the irradiation light. The phenomenon in which the diffraction efficiency changes depending on the pitch of the mask pattern and the polarization direction is called a waveguide effect (for example, see Japanese Patent No. 3750312). When a waveguide effect occurs, the intensity of light transmitted through the photomask varies in accordance with the pitch of the mask pattern. This causes an error in the line width or the like of the projection image of the mask pattern.